1. Field
The present disclosure relates to optical fiber technology and in particular to optical fiber amplifiers.
2. Background
Optical fiber communications has been the main enabler for realizing high capacity communication networks capable to transport massive amounts of data over a single fiber. The development of optical fiber amplifiers (OFA) gave a robust solution to the first capacity brick-wall of communication networks.
Up to now, OFAs continue to dominate the market of long-haul, metro and more recently to optical access networks that are aggressively expanding in terms of reach and bit-rate, with intra-data centre connectivity also rapidly gaining momentum. The traditional characteristics of cost sensitivity, power consumption and footprint continue to be critical, however the ability to design amplifiers with custom performance metrics such as input/output power levels, gain and noise figure are becoming increasingly important. A method for building low-power and small footprint OFAs that have different performance characteristics with sub-linear scaling of cost, power consumption and footprint is highly desirable. Moreover, the real-time control of their performance in terms of optical output power can critically assist networks or transmission links that are no longer static, but evolve in a dynamic way according to traffic, number of channels, number of fibers, optical output power required and in the case of access networks, number of clients per geographic area.
In long-haul networks, in spite of the continuous upgrades in new transmission systems, the traffic growth estimates suggest that in the next decade, optical fiber capacity and corresponding transport systems will not be able to cope with capacity demands. A potential solution to the theoretical capacity limit of the fiber is the use of space through new Space Division Multiplexed (SDM) systems. New generation of multi-core (MCF), few-mode (FMF) or multi-mode (MMF) fibers will allow scaling of the total fiber bandwidth on the one hand, while also requiring optical amplification per space channel or mode in a cost effective method. Hence, the requirement to employ multiple DWDM-enabled optical fiber amplifiers is expected to dramatically increase in future high-capacity transport systems.
In addition to terrestrial fiber-optic networks, optical fiber amplifiers with high energy efficiency and small volume are becoming key components in space communications for inter- and intra-satellite links and as sub-systems in various sensing and processing systems within satellite payloads. In the case where multiple optical fiber amplifiers are required within payload systems, a way to sub-linearly scale footprint and power consumption becomes critical in order to optimize overall satellite weight, dimensions and power consumption during the mission.
The state of the art design of fiber amplifiers involves a laser pump source, an active fiber span and passive fiber-pigtailed components for coupling optical pump to data signals. The replication of this solution for obtaining a large number of OFAs scales linearly or even non-linearly factoring in additional cooling and hardware real-estate. Hence, the design of scalable OFAs in terms of cost, size and power will play a key role in the development of future high capacity networks. The terms “multiple optical fiber amplifier” and “optical fiber amplifier array” are used interchangeably in this application.
FIG. 1 shows various types of typical optical fiber amplifiers. First type (110) is an optical fiber amplifier (OFA) in which the optical path is pumped in co-propagating mode by a pump laser component (112). OFA-1 (110) includes an optical path input port coupled at one end of optical isolator (113). Optical isolator (113) is coupled at the other end to a first input of optical coupler (114). The second input of optical coupler (114) is coupled to the output port of pump laser (112). The output of optical coupler (114) is coupled to one end of doped fiber (115). The other end of doped fiber (115) is coupled to the input of optical coupler (116). The first output of optical coupler (116) is coupled to one end of optical isolator (117). The other end of optical isolator (117) is the output of OFA-1 (110).
The second type is an optical fiber amplifier in which all the optical paths are pumped in counter-propagating mode by a single pump laser component. OFA-2 (120, 130) includes an optical path input port coupled at one end of optical isolator (123, 133). According to a first implementation of OFA-2 (120), optical isolator (123) is coupled at the other end to a first input of optical coupler (124). The output of optical coupler (124) is coupled to one end of doped fiber (125).
In a second implementation of OFA-2 (130), optical isolator (133) is coupled at the other end directly to one end of doped fiber (135). The difference between the first and the second implementation of OFA-2 is that there is no optical coupler after the optical isolator in the second implementation, compared to the first implementation. In both implementations, the other end of doped fiber (125, 135) is coupled to the input of optical coupler (126, 136). The first output of optical coupler (126, 136) is coupled to one end of optical isolator (127, 137). The second output of optical coupler (126, 136) is coupled to the output port of pump laser (122, 132. The other end of each optical isolator (127, 137) is the output of OFA-2 (120, 130).
The third type is an optical fiber amplifier in which the optical paths are pumped in both co- and counter-propagating mode using two pump lasers. OFA-3 (140) includes an optical path input port coupled to one end of optical isolator (143). Optical isolator (143) is coupled at the other end to a first input of optical coupler (144). The second input of optical coupler (144) is coupled to the output port of first pump laser (142a). The output of optical coupler (144) is coupled to one end of doped fiber (145). The other end of doped fiber (145) is coupled to the input of optical coupler (146). The first output of optical coupler (146) is coupled to one end of optical isolator (147). The second output of optical coupler (146) is coupled to the output port of second pump laser (142b). The other end of optical isolator (147) is the output of OFA-3 (140).
FIG. 2 shows a typical optical fiber amplifier array (OAA) (200). OAA (200) includes a set of n OFAs (210, 220, 230, 240) each OFA including at least one pump laser (212, 222, 232, 242). Although OAA is shown including OFAs of the first type, one skilled in the art may appreciate that OAA may include OFAs of any type as described with reference to FIG. 1.
It would be desirable to have a multiple OFA that is cost-effective, compact and power efficient each OFA having custom and independent output power, noise performance, topology and operating wavelength band specifications.